Any Football Helmet Hit Can Cause Potential Concussion

by John Gever John Gever,Contributing Writer, MedPage Today
December 07, 2007

Action Points

Explain that the study found no relationship between the impact or location of head impacts and concussion symptoms.

Explain that the implication is that high-impact blows will not necessarily produce concussions, nor will keeping impacts at moderate levels necessarily avoid them.

CHAPEL HILL, N.C., Dec. 7 -- Football concussions can occur from almost any type of head impact, irrespective of magnitude or location, at any level of play, including practice, researchers here said.

In a study of 76 collegiate players with accelerometers and telemetry devices embedded in their helmets, acute concussion symptoms were unrelated to both linear or rotational magnitude, Kevin M. Guskiewicz, Ph.D., and colleagues at the University of North Carolina reported online in three related papers in Neurosurgery.

They recorded 104,714 total impacts over the course of five seasons. Of these impacts, 11 players had one concussion and one had two.

"The uniqueness of our study is that it combines impact biomechanics captured in real-time with clinical measures of symptom severity, neurocognitive function, and postural stability captured within the acute period after concussive injury," they wrote.

They found that the threshold for concussion may be lower than originally predicted. On the other hand, many players had no concussions when the impacts were higher than the predicted threshold.

Fewer than 0.35% of impacts exceeding theoretical injury thresholds resulted in concussion, they noted. Also, coaches and sports medicine professionals should be aware that head impacts in helmets-only practices are as high as games or scrimmage. "There seem to be no 'light' days for football players."

Among the 13 players who had concussions, gravitational acceleration (g) impact magnitudes ranged from 60.51 g to 168.71 g, with six impacts on the top of the head, four on the front, two on the right, and one on the back.

Three of the concussions involved impacts of less than 80 g while in seven the impacts exceeded 100 g. The theoretical threshold is 70 to 75 g.

But linear regression showed no significant relationships between impact magnitude or location and severity of concussion symptoms, such as postural stability and neurocognitive function, the researchers said.

Another of the studies measured postural stability and cognition in players who did not report having concussion symptoms after receiving high (>90 g) or low (<60 g) impacts.

The researchers found no significant differences between the impact groups in cognitive function or balance. In fact, both groups showed significant improvements over pre-impact baseline scores in some cognitive tests, which the researchers attributed to learning effects.

"Our findings suggest that sustaining an impact greater than 90 g does not result in acute observable balance and neurocognitive deficits within 24 hours of sustaining the impact," the researchers said.

Other data collected by the group also cast doubt on the 70 to 75 g threshold. Out of 1,858 impacts of greater than 80 g, only seven resulted in concussion on the basis of players' self-reports of symptoms.

"It may be difficult to establish a threshold for concussive injury that can be applied to all football players," the researchers said.

Earlier research indicated that 5% of football players suffer concussions each season with 15% of those players sustaining a second concussion during the same season.

The researchers found that mean head impact magnitudes were significantly higher in helmet-only practices (22.47 g) and full-pad practices (22.65 g) than in games and scrimmages (21.12 g) (P<0.001).

Helmets-only practices accounted for 27.25% of the more than 57,000 head impacts recorded in the studies, compared to 22.57% in games and scrimmages and 50.17% in full-pad practices.

"Finally," the researchers wrote, "many sports medicine clinicians have anecdotally suggested that acceleration/deceleration magnitudes, particularly rotational acceleration, play a role in predicting injury severity. Our preliminary findings suggest that this may not be the case and calls for more research to be conducted to investigate how linear and rotational acceleration relate to measures of symptom severity, neurocognitive function, and postural stability in larger sample sizes across the entire recovery period."

The studies were supported by the CDC.

No financial disclosures were reported.

Reviewed by Zalman S. Agus, MD Emeritus Professor University of Pennsylvania School of Medicine

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